GREENE: Ford Motor Company will reduce the fuel economy sticker on its new C-Max hybrid to 43 miles per gallon, down from its earlier estimate of 47.

As Michigan Radio's Tracy Samilton reports, the change has generated a new review of fuel economy testing standards.

TRACY SAMILTON, BYLINE: Ford wants to be a fuel economy leader, rivaling Toyota. Its ads for the C-Max compared its fuel economy favorably to the Prius. Now, those ads will have to be yanked.

Jake Fisher is with Consumer Reports, which early on questioned the C-Max mpg. Fischer says one problem could be that the EPA's fuel economy tests factor in a lot of stop-and go driving.

JAKE FISHER: But if you're just cruising along at 70, you're not going to get anywhere near those numbers.

SAMILTON: Here's another problem. The EPA's Chris Grundler says Ford originally didn't even put the C-Max through the tests. As permitted by EPA rules, Ford used its Fusion hybrid to stand in for the C-Max - because both vehicles are the same weight and have the same power train. That generally works fine.

CHRIS GRUNDLER: This did not work for the Ford C-Max.

SAMILTON: Grundler says the agency will review its standards to make sure the fuel economy sticker for a hybrid is as accurate as for a non-hybrid.

GRUNDLER: We're going to see more of this in the future, which is why we want to nip this in the bud.

SAMILTON: The mileage downgrade will be costly for Ford which will send a $550 rebate to all 32,000 of its C-Max customers.